It is generally known to use electrochemical sensors, often also referred to as lambda probes, to determine, for example, the oxygen content of exhaust gases, in particular of exhaust gases of internal combustion engines. Two principal variants of these exist. They are the "finger" probe, as described, for example, in U.S. Pat. No. 5,310,575; and as the second embodiment the "plate" probe, as described, for example, in U.S. Pat. No. 5,529,677. All the known sensors of this kind are based on the principle of the oxygen concentration chain, with an ion-conducting solid electrolyte. They contain as the probe body, for example in the case of the "finger" probe, a tube, closed at one end and made of an ionically conducting material, for example yttrium oxide-stabilized zirconium dioxide (YSZ), on the outer surface of which are located, facing the exhaust gas, a conductive path and a measurement electrode which can consist, for example, of platinum cement. In the case of the "plate" probe, the ceramic of the rod- or plate-shaped solid electrolyte consists of the same material, and here again conductive paths and a measurement electrode, which can also consist, for example, of platinum cement, are arranged on the ceramic on the surface facing the exhaust gas.
The conductive path and the measurement electrode layer or layers are very thin in these sensors, and although they generally bear additional ceramic cover layers and/or protective layers, they are nevertheless subject, after extended use, to corrosive attack by some of the exhaust gas constituents, e.g. soot and compounds of lead, phosphorus, nitrogen, and sulfur. In addition, the conductive paths and the measurement electrode layers tend, under unfavorable conditions, to detach from the ceramic element.
Until now, no satisfactory method had been proposed for determining the adhesion of such material layers, i.e. of the electrodes and the conductive path layers and any cover layers that might be present, on such ceramic elements, so as thereby to monitor production in qualitative terms.